The present invention concerns a procedure and apparatus for controlling the surface mass distribution of a paper web formed on a dry paper machine, the procedure being utilizing the suction air recirculated to the former.
In prior art devices, former comprises rotating drums into which a fiber flow is introduced crosswise through the ends of the drums. Under the former is disposed a moving wire, through which air is drawn, whereby the particle-laden air forms a material web on the wire. The mantles of the drums are provided with exit holes through which fibers are spread onto the material web, but owing to the mode of distribution, no uniform distribution of the fiber flow from the exit holes of the drums is achieved: the profile presents errors up to 10%. In the present invention, the air recirculation principle disclosed in Finnish application of Bothas, Ser. No. 853043, assigned to Yhtyneet Paperitehtaat Oy Jylhavaara, filed Aug. 8, 1985, parallel to the application in hand, is utilized. In that connection, the air which is drawn into the suction box is returned to the upper part of the former as uniformly as possible.